poj 2763 Housewife Wind(树链拆分)

题目大意：给定一棵树，然后2种操作：
0 u：输出路径s到u的权值和，而且s变成u
1 i w：节点i添加w
解题思路：树链剖分，然后用线段树维护，单点改动区间查询。
#include <cstdio>

#include <cstring>

#include <algorithm>

using namespace std;

const int maxn = 100005;

int N, Q, S, ne;

int first[maxn], jump[maxn * 2];

int id, far[maxn], son[maxn], cnt[maxn], dep[maxn], top[maxn], idx[maxn];

struct Edge {

    int u, v, w;

    void set (int u, int v, int w) {

        this->u = u;

        this->v = v;

        this->w = w;

    }

}ed[maxn * 2];

void dfs_fir (int u, int pre, int d) {

    far[u] = pre;

    dep[u] = d;

    cnt[u] = 1;

    son[u] = 0;

    for (int i = first[u]; i + 1; i = jump[i]) {

        int v = ed[i].v;

        if (v == pre)

            continue;

        dfs_fir(v, u, d+1);

        cnt[u] += cnt[v];

        if (cnt[son[u]] < cnt[v])

            son[u] = v;

    }

}

void dfs_sec(int u, int rot) {

    top[u] = rot;

    idx[u] = id++;

    if (son[u])

        dfs_sec(son[u], rot);

    for (int i = first[u]; i + 1; i = jump[i]) {

        int v = ed[i].v;

        if (v == far[u] || v == son[u])

            continue;

        dfs_sec(v, v);

    }

}

inline void add_Edge(int u, int v, int w) {

    ed[ne].set(u, v, w);

    jump[ne] = first[u];

    first[u] = ne++;

}

#define lson(x) ((x)<<1)

#define rson(x) (((x)<<1)|1)

typedef long long ll;

int lc[maxn << 2], rc[maxn << 2];

ll s[maxn << 2];

inline void pushup(int u) {

    s[u] = s[lson(u)] + s[rson(u)];

}

void build (int u, int l, int r) {

    lc[u] = l;

    rc[u] = r;

    s[u] = 0;

    if (l == r)

        return;

    int mid = (l + r) / 2;

    build(lson(u), l, mid);

    build(rson(u), mid + 1, r);

    pushup(u);

}

void modify (int u, int x, int w) {

    if (lc[u] == x && rc[u] == x) {

        s[u] = w;

        return;

    }

    int mid = (lc[u] + rc[u]) / 2;

    if (x <= mid)

        modify(lson(u), x, w);

    else

        modify(rson(u), x, w);

    pushup(u);

}

ll query(int u, int l, int r) {

    if (l <= lc[u] && rc[u] <= r)

        return s[u];

    ll ret = 0;

    int mid = (lc[u] + rc[u]) / 2;

    if (l <= mid)

        ret += query(lson(u), l, r);

    if (r > mid)

        ret += query(rson(u), l, r);

    return ret;

}

void init () {

    ne = 0;

    id = 1;

    int u, v, w;

    memset(first, -1, sizeof(first));

    for (int i = 0; i < N - 1; i++) {

        scanf("%d%d%d", &u, &v, &w);

        add_Edge(u, v, w);

        add_Edge(v, u, w);

    }

    dfs_fir(1, 0, 0);

    dfs_sec(1, 1);

    build(1, 1, N);

    for (int i = 0; i < N - 1; i++) {

        if (dep[ed[i*2].u] < dep[ed[i*2].v])

            swap(ed[i*2].u, ed[i*2].v);

        modify(1, idx[ed[i*2].u], ed[i*2].w);

    }

}

ll solve (int u, int v) {

    ll ret = 0;

    int p = top[u], q = top[v];

    while (p != q) {

        if (dep[p] < dep[q]) {

            swap(p, q);

            swap(u, v);

        }

        ret += query(1, idx[p], idx[u]);

        u = far[p];

        p = top[u];

    }

    if (u == v)

        return ret;

    if (dep[u] > dep[v])

        swap(u, v);

    ret += query(1, idx[son[u]], idx[v]);

    return ret;

}

int main () {

    while (scanf("%d%d%d", &N, &Q, &S) == 3) {

        init();

        int k, u, w;

        while (Q--) {

            scanf("%d%d", &k, &u);

            if (k) {

                scanf("%d", &w);

                modify(1, idx[ed[u*2 - 2].u], w);

            } else {

                printf("%lld\n", solve(S, u));

                S = u;

            }

        }

    }

    return 0;

}